Studies are being made of the lipid and fatty acid composition of male reproductive tissue in several species of animals and of the metabolism of these lipids. The latter include the biosynthesis and interconversion of fatty acids using both in vivo and in vitro methods. Alterations in the chemistry and in the metabolism of such lipids brought about by various factors such as age, diet, pathological conditions and hormonal influences are being studied. The chemical and biochemical observations are supplemented with histological examination of the tissues.